Blade lifting device for power hack saws



May 31, 1949.

1'. A. PODHAJSKY BLADE LIFTING DEVICE FOR POWER HACK SAWS 2 Sheets- Sheet 1 Filed June 7, 1945 May 31, 1949. T. A. PODHAJSKY BLADE LIF'IING DEVICE FOR POWER HACK SAWS 2 Sheets-Sheet 2 Filed June 7, 1945 Poi 720 715749 Patented May 31, 1949 UNITED STATES PATENT OFFICE BLADE LIFTING DEVICE FOR POWER HACK SAWS 1 Claim. 1

This invention relates to new and useful improvements in blade lifting devices for power hack saws.

The primary object of my invention is to provide a novel mechanism of this character that will lift the blade off the work at the commencement of and during the return stroke of the saw, thereby saving wear on the saw blades and obtaining smoother action, while at the same time substantially reducing the power required to operate the saw.

A further object of my invention is to provide a blade lifting device for power hack saws that is simple and economical in construction and highly efiicient and durable in operation.

With the foregoing and other objects in view that will appear as the nature of my invention is better understood, the same consists in the novel features of construction, combination and arrangement of parts illustrated in the accompanying drawings and more particularly pointed out in the appended claim.

In the accompanying drawings, which are for illustrative purposes only and are therefore not drawn to scale:

Figure l is a side elevation, illustrating the application of my invention.

Figure 2 is a plan view.

Figure 3 is a vertical transverse section, taken on line 3-3 of Figure 1, looking in the direction indicated by the arrows.

Figure 4 is a similar view, taken on line 4-4 of Figure 1, looking in the direction indicated by the arrows, and Figure 5 is an enlarged detail longitudinal section, taken on line 55 of Figure 2.

Referring to the drawings for a more particular description of my invention, and in which darwings like parts are designated by like reference characters throughout the several views, the numeral I designates a horizontal drive shaft, journaled in a suitable upright support or bearing 2, at one end of the base 3. One end of the drive shaft l is provided with a crank arm 4, connected to the inner end 5 of the inverted U-shaped saw frame 6, by the longitudinally disposed link 1. The saw frame 5 carries the usual hack saw 8, and is provided with the cross head 9, which reciprocates back and forth on the longitudinal guide bar Ill. The guide bar It is secured at its inner end, as at I I, to the head I2 of the oscillating yoke I3, mounted on the drive shaft.

In carrying out my invention, a cam or eccentric I4, is keyed or fixed to the drive shaft, adjacent the crank arm 4, and this cam or eccentric works against the upper edge and one end of the.

lifting arm I5, pivoted intermediate its ends, as at It, to the standard It on the base 3. The opposite end of the lifting arm I5 is provided with a smooth perpendicularly disposed rod II, whose upper end I8 extends through a corresponding opening I9, in the shank 2c of the counterweighted dog 2|, pivoted, as at 22, to a supporting arm or bracket 23, carried by the head I2 of the yoke I3.

In practice, the upper end i 3 of the perpendicularly disposed rod IT slides downwardly through the opening I9 in the shank 20 of the counterweighted dog 2| during the cutting stroke of the hack saw, but on the return stroke, the inner end of the pivoted lifting arm I5 is depressed by the cam M, and through the medium of the perpendicularly disposed rod I I and dog 2 I, lifts the saw off the work, indicated by the numeral 24. This lifting action is obtained at the commencement of and durin the return stroke of the saw because of the fact that the upper end of the rod I'l binds against the apertured end 20 of the dog 2| and the weighted end or head 25 of the latter abuts against the top of the head I2 of the oscillating yoke I3 supported on the drive shaft.

The lower end of the rod I1 is formed with a right-angularly bent portion 26 adapted to engage any one of a series of transverse openings 21, formed in the outer end of the pivoted lifting arm I5. By virtue of this adjustment, the blade can be caused to lift only enough to prevent drag on the return stroke.

It is claimed that the application of my invention will save wear on the saw blade and obtain smoother action, while at the same time substantially reduce the power required to operate the saw.

From the foregoin description taken in connection with the drawings, it is thought that the construction, operation and advantages of my invention, will be readily understood Without requiring a more extended explanation.

Various changes in the form, proportions and minor details of construction may be resorted to without departing from the principles or sacrificing any of the advantages of my invention, as defined in the appended claim.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

In a blade lifting device for power hack saws, a base, a horizontal drive shaft, mounted on the base, a horizontal lifting arm pivoted to the base, said arm provided in one end with a series of transverse openings, a cam carried by said drive shaft and working against the opposite end of the lifting arm, said cam adapted to depress said last mentioned end of the lifting arm once during each revolution of the drive shaft, a reciprocating saw frame, a saw mounted in said saw frame, a yoke pivotally supported on the drive shaft and carrying said saw frame, a cross head secured to the saW frame, a guide bar carried by the oscillating yoke for the cross head, a supporting arm extending from the top of the yoke, a dog pivoted intermediate its ends to said supporting arm, said dog comprising an apertured shank formed at one end with a weighted head, a vertically disposed inclined rod adjustably connected at its lower end to the apertured end of the lifting arm and arranged with its upper end working through the apertured shank of the dog, said inclined rod and dog co-acting to lift the blade oii the work when the second mentioned end or the lifting arm is depressed by the cam during the return stroke of the saw.

THEODORE A. PODHAJSKY.

4 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 865,269 Renkenberger Sept. 3, 1907 935,665 Lanfair Oct. 5, 1909 1,056,880 Berry Mar. 25, 1913 1,146,572 Humpage July 13, 1915 1,269,883 Wardman June 18, 1918 1,563,870 Reinhardt et al Dec. 1, 1925 FOREIGN PATENTS Number Country Date 563,758 France Oct. 4, 1923 

